It's always hard because when you contrive possible examples of how it goes wrong, every single example sounds contrived because of course they are contrived.

Sure one day your printer might start spewing random json code meant for some microservice of the rightful IP owner.

Sure the IP's might be owned by the Air Force and one day they might start getting traffic from your pos ipad that they decide looks like an attempt to attack one of their internal secret networks...

Sure one day traffic meant to go to your printer ends up flooding and dossing a windmill controller, preventing the rightful operators from turning it the right direction during bad weather and causing $25M damage...

And of course the real failures are more like, only people from the Maldives can't send email to your email server, a failure with no impact.